(57) The invention relates to resonator structures of radio communication apparatus, especially
bulk acoustic wave filter structures. According to the invention, a bulk acoustic
filter structure is constructed with a lattice configuration, in which two of the
filters have a different area than other two for creating very steep passband edges
in the frequency response of the filter. Preferably, the filter structure further
comprises a second lattice structure for increasing the stopband rejection ratio of
the filter structure, and for allowing the use of a simple mechanical structure. The
cascaded configuration allows the construction of the filter structure in such a way,
that the electrodes of the input and output port are at the same layer, thereby removing
the need to make vias in the piezoelectric layer, which results in considerable simplification
of the manufacturing process. Preferably, an acoustical mirror structure is used as
the acoustical isolation in order to further simplify the mechanical structure of
the filter structure.
|
|
